3:45 PM - 4:00 PM
[ACG41-07] Quantitative analysis of DOM release from macroalgae bed at community level
Keywords:macroalgae bed, Dissolved organic matter, carbon sequestration
Capacity of carbon sequestration of macroalgal beds have been recently focused as a measure of global warming. Two major processes; transport of algal body and release of dissolved organic matter (DOM) would contribute to sequestration of carbon to deep sea. Since most of studies on macroalgal DOM is limited to the species with large algal body such as kelp, analysis at community level has been rarely studied. Release of DOM is mainly attributed to active extracellular excretion to ambient waters and secretion of intracellular materials as a consequence of damage on algal body. Therefore, non-destructive method is required to quantify DOM release in natural community with diverse algal species.
We deployed lava tile on seafloor, and then macroalgae recruited on that. It takes long duration (e.g., several months) to use the tile for experiment, but retrieving tiles allow us to transport the community without any disturbance. The location of our survey is Oura bay, Shimoda, Izu Peninsula, Japan, and the tiles were deployed nearby the coast. There are wide variety of macroalgal species in Shimoda (more than 200 species), but in recent years, degradation of kelp forest and shift of flora toward coralline algae and low-profile algae have been reported. We deployed tiles (13 × 13 cm) on August 2022. The flora was monitored to show community succession. On February 2023, three tiles were retrieved, and they were incubated under a light condition (200 μmol m-2 s-1). We collected sub-samples with intervals of 2 hours. Seawater samples were filtered with Glassfiber filter, and DOC (Dissolved Organic Carbon) concentrations were measured with total carbon analyzer (TOC-V, Shimadzu).
The surfaces of tiles were covered by coralline algae, low-profile algae and soft sediments. We identified 24 species of macroalgae, and dominant group was Rhodophyceae. DOC concentrations were significantly increased with time, and DOC release rates were 6.65 ± 1.31 mg C m-2 h-1. In the present study, we successfully quantify the DOC release rate of macroalgal community by using recruiting tiles. Comparing some previous studies on kelp providing DOC release rate per community area (10-240 mg C m-2 h-1; Mohammed et al. 2004; Wada et al. 2008), the estimate in the present study was lower values. We consider an underestimation of DOM release rate because macroalgal community dominated by low-profile algae would be still under succession stage.
We deployed lava tile on seafloor, and then macroalgae recruited on that. It takes long duration (e.g., several months) to use the tile for experiment, but retrieving tiles allow us to transport the community without any disturbance. The location of our survey is Oura bay, Shimoda, Izu Peninsula, Japan, and the tiles were deployed nearby the coast. There are wide variety of macroalgal species in Shimoda (more than 200 species), but in recent years, degradation of kelp forest and shift of flora toward coralline algae and low-profile algae have been reported. We deployed tiles (13 × 13 cm) on August 2022. The flora was monitored to show community succession. On February 2023, three tiles were retrieved, and they were incubated under a light condition (200 μmol m-2 s-1). We collected sub-samples with intervals of 2 hours. Seawater samples were filtered with Glassfiber filter, and DOC (Dissolved Organic Carbon) concentrations were measured with total carbon analyzer (TOC-V, Shimadzu).
The surfaces of tiles were covered by coralline algae, low-profile algae and soft sediments. We identified 24 species of macroalgae, and dominant group was Rhodophyceae. DOC concentrations were significantly increased with time, and DOC release rates were 6.65 ± 1.31 mg C m-2 h-1. In the present study, we successfully quantify the DOC release rate of macroalgal community by using recruiting tiles. Comparing some previous studies on kelp providing DOC release rate per community area (10-240 mg C m-2 h-1; Mohammed et al. 2004; Wada et al. 2008), the estimate in the present study was lower values. We consider an underestimation of DOM release rate because macroalgal community dominated by low-profile algae would be still under succession stage.